What kinds of jobs exist that blend mathematics and ecology, outside of academia? Are they in government and if so, what agencies? Are they in consulting? Private industry?

I have a master's in mathematics and 3 years of work experience in environmental consulting (wetlands, streams, wildlife). Is a master's in math enough to get into jobs that apply math to ecology, or is a PhD necessary? What is the job market like for these jobs?

Definitely the EPA and 3rd party consultant groups have roles that fit your requirements but the level of math you'll find there is almost certainly not what you'd see in academics. I'd target the groups the EPA leverages as consultants. They are the ones who walk in with the data and build the case. The EPA tends to be more of an aggregator and policy enforcer so they don't really focus on the research in-house.

Regarding the job market part of your question.. that's going to be heavily dependent on which aspect of ecology you're looking to target so it's hard to answer w/o more specific information.